it would be a 283 if original, and will prolly have a governor in a big truck - they didn't make a "3 ton", higher GVW was just a 1.5T with bigger wheels/tires, more springs, and a fish plate on the frame from just under the cab to the front hanger of the rear springs, which was called a 2T - problem will be that the diff ratios will be about 7:1, top speed not great! and not likely to have a 2spd if 4x4
Bill